Many food and beverage products contain nutritive sweeteners such as sucrose (generally referred to as ‘sugar’ or ‘table sugar’), glucose, fructose, corn syrup, high fructose corn syrup and the like. Such sweeteners supply not only sweetness to the food and beverage products, but also bulk, texture and desirable functional properties such as browning, humectancy, freezing point depression and the like. They also produce a favorable sensory response, for example in terms of quality of sweetness, lack of bitterness and off taste, desirable temporal profile and desirable mouthfeel.
Although desirable in terms of taste and functional properties, excess intake of nutritive sweeteners, such as sucrose, has long been associated with an increase in diet-related health issues, such as obesity, heart disease, metabolic disorders and dental problems. This worrying trend has caused consumers to become increasingly aware of the importance of adopting a healthier lifestyle and reducing the level of nutritive sweeteners in their diet.
In recent years, there has been a movement towards the development of replacements for nutritive sweeteners, with a particular focus on the development of low or zero-calorie sweeteners. An ideal replacement for a nutritive sweetener is a sweetener that has the same desirable taste characteristics and functional properties as the nutritive sweetener, but which also has fewer or substantially no calories. Aiming to meet this growing need, the market has been flooded with possible candidates to replace conventional nutritive sweeteners. Unfortunately, however, many of the low or zero calorie replacements offered on the market lack one or all of the necessary characteristics, and often exhibit bitterness or off-taste. Therefore, many of the proposed sweeteners are not an ideal replacement for nutritive sweeteners.
One proposed alternative to nutritive sweeteners is allulose (also known as D-psicose). Allulose is known as a “rare sugar”, since it occurs in nature in only very small amounts. It provides around 70% of the sweetness of sucrose, but only around 5% of the calories (approximately 0.2 kcal/g). It may therefore essentially be considered to be a ‘zero calorie’ sweetener.
In view of its scarcity in nature, production of allulose relies on the epimerization of readily available fructose. Ketose-3-epimerases can interconvert fructose and allulose, and various ketose-3-epimerases are known for carrying out this conversion.
U.S. Pat. No. 8,030,035 and PCT Publication No. WO2011/040708 disclose that D-psicose can be produced by reacting D-fructose with a protein derived from Agrobacterium tumefaciens, and having psicose 3-epimerase activity.
US Patent Publication No. 2011/0275138 discloses a ketose 3-epimerase derived from a microorganism of the Rhizobium genus. This protein shows a high specificity to D- or L-ketopentose and D- or L-ketohexose, and especially to D-fructose and D-psicose. This document also discloses a process for producing ketoses by using the protein.
Korean Patent No. 100832339 discloses a Sinorhizobium YB-58 strain which is capable of converting fructose into psicose (i.e. allulose), and a method of producing psicose using a fungus body of the Sinorhizobium YB-58 strain.
Korean Patent Application No. 1020090098938 discloses a method of producing psicose using E. coli wherein the E. coli expresses a polynucleotide encoding a psicose 3-epimerase.
Allulose is present in processed cane and beet molasses, steam treated coffee, wheat plant products, and high fructose corn syrup. D-allulose is the C-3 epimer of D-fructose and the structural differences between allulose and fructose result in allulose not being metabolized by the human body to any significant extent, and thus having “zero” calories. Thus, allulose is thought to be a promising candidate as a replacement for nutritive sweeteners and as a sweet bulking agent, as it has no calories and is reported to be sweet while maintaining similar properties to sucrose.
One of the most recently proposed alternatives to table sugar is Monk Fruit extract. Monk fruit is a fruit from the plant species Siraitia grosvenorii, of the Cucurbitaceae family, and is a type of small melon which grows exclusively in tropical and subtropical regions of Southeast Asia. This fruit is also known as “Luo han guo”, is roughly 200 times sweeter than cane sugar, and provides calorie-free sweetness. The main sweet components of Monk Fruit leading to its sweet taste are known as mogrosides. Mogrosides are members of the family of triterpene glycosides. The sweet taste of mogrosides is thought to be related to the number of glucose units present in the mogroside. Examples of mogrosides found in Monk Fruit are Mogroside V, Mogroside IV, Mogroside VI, Oxomogroside V, Mogroside IIIE, and Siamenoside I.
However, more recent studies have shown that some mogrosides may exhibit an off-taste and a less desirable temporal profile. Furthermore, allulose may have limitations in use due to cost and digestive tolerance in some applications. Therefore, there is a need to provide an improved replacement for sucrose and other nutritive sweeteners that has low or zero-calories and is without limitations in use, but which also has taste characteristics similar to those of sucrose.